Many injection devices of the above type (i.e. where a syringe is moved in distal direction during the injection operation) are particularly easy to use since the entire injection process (causing the needle of the syringe to penetrate the skin and the dose to be injected) can be triggered simply by pushing one button. One example of such an injection device is disclosed in WO 03/011378, which is incorporated herein by reference in its entirety. Whilst this device works well, the present inventors have appreciated at least two drawbacks with this device: there is no provision for adjusting the dose to be injected, and there is also no provision for priming the syringe. By way of explanation, “priming” refers to the process of expelling from the syringe any air and perhaps a small amount of fluid which is initially contained in the syringe. The present invention has been made with a view to overcoming these drawbacks. However, it will be appreciated, on consideration of the present specification, that the various aspects of the invention find application also in other types of injection/substance delivery devices.
Whilst dose adjustment and a priming function are generally known (the attention of the reader is directed to WO 2005/044346 and WO 2005/046770, also incorporated herein by reference in their entirety), it will be appreciated that thus far there has not been any attempt to provide the injection device of e.g. WO 03/011378 with an adjustment and/or priming function. As will be appreciated, the way in which the adjustment and the priming function pursuant to the present invention work is quite different from any adjustment or priming function disclosed in WO 2005/046770 and WO 2005/044346. This is why in particular the dose adjustment mechanism is useful in its own right, that is, it can be used with a range of other injection devices, not limited to injection devices in which a syringe is moved in distal direction during the injection process.
Aspects of the invention are set out in the independent claims.